State data show contaminated groundwater near all 13 N.C. coal-ash ponds owned by Duke Energy and Progress Energy, an environmental group said Tuesday.

Ash, left by coal-burning power plants, is loaded with metals that can be toxic at high levels. It's often mixed with water and piped into open basins, a practice under scrutiny since a ruptured dike in Tennessee spilled 5 million cubic yards of sludge in December.

The analysis by Boone-based Appalachian Voices shows ash can also seep into groundwater and, the group said, also needs more oversight by regulators. The report detailed 681 instances in the testing of the ponds in which pollutants exceeded state groundwater standards.